Field of the Disclosure
Embodiments relate to an organic light emitting display device, including a method of driving an organic light emitting display device that prevents a sensing line from being discerned by a real-time sensing process for external compensation, to thereby improve picture quality.
Discussion of the Related Art
With reference to FIG. 1, which is a circuit diagram illustrating a pixel of an organic light emitting display device according to the related art, each pixel of a display panel may include a first switching TFT (ST1), a second switching TFT (ST2), a driving TFT (DT), a capacitor (Cst), and an organic light emitting diode (OLED).
The first switching TFT (ST1) may be switched by a scan signal (or gate driving signal) supplied to a gate line GL. As the first switching TFT (ST1) is turned on, a data voltage Vdata supplied to a data line DL is accordingly supplied to the driving TFT (DT).
The driving TFT (DT) may be switched by the data voltage Vdata supplied from the first switching TFT (ST1). A data current I_oled flowing to the organic light emitting diode (OLED) may be controlled by switching the driving TFT (DT).
The capacitor (Cst) may be connected between gate and source terminals of the driving TFT (DT), wherein the capacitor (Cst) stores a voltage corresponding to the data voltage Vdata supplied to the gate terminal of the driving TFT (DT), and turns on the driving TFT (DT) by the use of stored voltage.
A first driving power VDD, which is applied through a power line PL, may be supplied to the source terminal of the driving TFT (DT). The organic light emitting diode OLED may be electrically connected between a cathode power source (VSS) and the source terminal of the driving TFT (DT), wherein the organic light emitting diode (OLED) may emit light in response to the data current (I_oled) supplied from the driving TFT (DT).
The organic light emitting display device according to the related art may control an intensity of the data current (I_oled) flowing from the first driving power (VDD) to the organic light emitting diode (OLED) by switching the driving TFT (DT) according to the data voltage (Vdata), whereby the organic light emitting diode (OLED) emits light and thereby displays an image.
However, in the organic light emitting display device according to the related art, the characteristics of the driving TFT (DT), for example, threshold voltage (Vth) and mobility, may be differently shown by each pixel due to non-uniformity in a process of manufacturing the TFT. Accordingly, even though the data voltage Vdata may be identically applied to the driving TFT (DT) for each pixel, it can be difficult to realize uniform picture quality due to a deviation of the current flowing in the organic light emitting diode (OLED).
In order to overcome this problem, there may be provided a second switching TFT (ST2). As the second switching TFT (ST2) is switched by a sensing signal applied to a sensing signal line (SL), the data current (I_oled) supplied to the organic light emitting diode (OLED) is supplied to an analog-to-digital converter (ADC) of a drive integrated circuit (drive IC). In this case, the sensing signal line (SL) can be formed in the same direction as the gate line (GL).
After completing a process of manufacturing the display panel, variations in the characteristics among the driving TFTs (DT) of all the pixels may cause spots or stains on a screen. In order prevent the spots or stains, it is required to measure and compensate for the threshold voltage (Vth) and mobility of the driving TFT (DT) of all the pixels before a product shipment.
FIG. 2 illustrates a method of driving displaying and sensing modes in the organic light emitting display device according to the related art.
With reference to FIG. 2, in the driving mode, an image may be displayed by programming the data voltages Vdata based on video data from the first data line to the last data line for a time period of N frames.
In the sensing mode, the sensing signal may be supplied to one or more sensing lines of all the sensing lines for a blank period between an (n)th frame and an (n+1)th frame (for example, if driven by 120 Hz, about 360 us), thereby performing a real-time sensing process.
The real-time sensing process may have the following steps.
First, a sensing pre-charging voltage (Vpre_s) may be supplied to all the pixels or some of the pixels (P) performed with the sensing process for the blank period between the (n)th frame and the (n+1)th frame. By selectively switching the second switching TFT (ST2) in all the pixels or some of the pixels, a voltage charged in a reference voltage line (RL) can be detected. Then, the detected voltage may be converted into compensation data corresponding to threshold voltage and mobility of the driving TFT (DT) for each pixel (P).
Thereafter, the pixels may be sequentially sensed by each one horizontal line during the plurality of blank periods, to thereby sense the threshold voltage and mobility of the driving TFT (DT) for all the pixels of the display panel. Then, the data voltage (Vdata) applied to the pixel can be compensated by the use of compensation voltage based on the detected threshold voltage/mobility. In this case, the compensation data may be generated based on the threshold voltage/mobility detected by sensing.
FIG. 3 illustrates that the sensing line on the screen may be discerned by the real-time sensing process.
In FIG. 3, the current is not flowing in the pixel (P) performed with the sensing process during the blank period. A luminance of the pixels (P) positioned along the line in which the sensing process is performed may be decreased by 5% in comparison to that of the normal line. As the real-time sensing process is sequentially performed by each one horizontal line, the sensing line on the screen is discerned.